content: /*
   * Copyright 2017 David Karnok
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package hu.akarnokd.reactive4javaflow.impl.operators;
  
  import hu.akarnokd.reactive4javaflow.*;
  import hu.akarnokd.reactive4javaflow.functionals.CheckedBiFunction;
  import hu.akarnokd.reactive4javaflow.impl.*;
  
  import java.util.Objects;
  import java.util.concurrent.*;
  
  public final class FolyamReduceSeed<T, R> extends Esetleg<R> {
  
      final Folyam<T> source;
  
      final Callable<? extends R> initialSupplier;
  
      final CheckedBiFunction<R, ? super T, R> reducer;
  
      public FolyamReduceSeed(Folyam<T> source, Callable<? extends R> initialSupplier, CheckedBiFunction<R, ? super T, R> reducer) {
          this.source = source;
          this.initialSupplier = initialSupplier;
          this.reducer = reducer;
      }
  
      @Override
      protected void subscribeActual(FolyamSubscriber<? super R> s) {
          R seed;
  
          try {
              seed = Objects.requireNonNull(initialSupplier.call(), "The initialSupplier returned a null value");
          } catch (Throwable ex) {
              EmptySubscription.error(s, ex);
              return;
          }
  
          source.subscribe(new ReduceSeedSubscriber<>(s, seed, reducer));
      }
  
      static final class ReduceSeedSubscriber<T, R> extends DeferredScalarSubscription<R> implements FolyamSubscriber<T> {
  
          final CheckedBiFunction<R, ? super T, R> reducer;
  
          Flow.Subscription upstream;
  
          ReduceSeedSubscriber(FolyamSubscriber<? super R> actual, R seed, CheckedBiFunction<R, ? super T, R> reducer) {
              super(actual);
              value = seed;
              this.reducer = reducer;
          }
  
          @Override
          public void onSubscribe(Flow.Subscription subscription) {
              upstream = subscription;
              actual.onSubscribe(this);
              subscription.request(Long.MAX_VALUE);
          }
  
          @Override
          public void onNext(T item) {
              if (getPlain() != CANCELLED) {
                  try {
                      value = Objects.requireNonNull(reducer.apply(value, item), "The reducer returned a null value");
                  } catch (Throwable ex) {
                      value = null;
                      upstream.cancel();
                      error(ex);
                  }
              }
          }
  
          @Override
          public void onError(Throwable throwable) {
              value = null;
              error(throwable);
          }
  
          @Override
          public void onComplete() {
              complete(value);
          }
  
          @Override
          public void cancel() {
              super.cancel();
              upstream.cancel();
          }
      }
  }
  